JPH02248977A - Fixing device - Google Patents

Abstract

PURPOSE:To contrive the coincidence of the circumferential speed of fixing rolls of a fixing device with the circumferential speed of a photosensitive drum by independently providing a driving device for driving the fixing rolls, detecting the revolving speed of the fixing rolls and controlling the driving device. CONSTITUTION:The driving device 30 which is independently provided is controlled by detecting the revolving speed of the fixing rolls 20 and 21 by using a circumferential speed encoder 40 of the fixing rolls 20 and 21. Therefore, when some changes occurred in the circumferential speed of the fixing rolls 20 and 21, the circumferential speed of the image carrier is maintained at the fixed value. Thus, the image carrier circumferential speed controlled at the fixed value and the circumferential speed of the fixing rolls 20 and 21 are controlled so as to be coincident with each other.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a fixing device for an image forming apparatus such as an electrophotographic copying machine or an electrophotographic printer that employs an electrophotographic process.

(Prior Art) In an image forming apparatus that employs an electrophotographic process, an electrostatic latent image formed on a photosensitive drum, which is an image carrier, is visualized by a developing device to form a toner image.

An image is generally formed by transferring the toner image onto a transfer paper and fixing the toner image on the transfer paper by a fixing device.

The fixing device transports the transfer paper, on which the toner image has been transferred from the photosensitive drum, while sandwiching it between a pair of fixing rollers that are equipped with a heater or the like and rotate in pressure contact with each other.
The toner image on the transfer paper is heated and pressurized to melt it and fix it as a permanent image on the transfer paper.

In small-sized electrophotographic printers, the fixing roller of the fixing device is often driven by a single main motor along with the photosensitive drum and the developing sleeve of the developing device, whereas in medium-sized electrophotographic printers.

The fixing roller, along with the developing sleeve, etc., is driven by one main motor, but in most cases the photosensitive drum is driven by a separate tram motor.A tachometer generator is connected to the main motor and drum motor in most cases. There are known devices that are controlled to rotate at a constant speed.

In particular, since the transfer paper that has completed the transfer operation on the photosensitive drum immediately enters the fixing device, the circumferential speed of the photosensitive drum, that is, the speed of the transfer paper passing through the photosensitive drum.

It is preferable that the circumferential speed of the fixing roller, that is, the speed of the transfer paper passing between the fixing rollers, be equal. This is because the photosensitive drum and the fixing device are relatively close to each other, and depending on the size of the transfer paper, Although the leading edge of the transfer paper is inside the fixing device, the trailing edge may still be receiving toner image transfer from the photosensitive drum. When transferring a toner image, if the transfer density fluctuates in the direction of movement of the transfer paper, or if the circumferential speed of the transfer roller is smaller than the circumferential speed of the photosensitive drum, the intermediate portion of the transfer paper may loop and the loop portion of the transfer paper may change. This is because the toner image contacts the protective cover of the process cartridge, causing an inconvenience in that the toner image before fixing is significantly damaged by "scratching" or the like.

(Problem II to be Solved by the Invention) However, in the fixing device of the above-mentioned prior art, the fixing roller is driven by the main motor via gears, chains, etc., so backlash between the gears, rattling of the chain, etc. As a result, the circumferential speed of the fixing roller, especially the circumferential speed of the nip area where the pair of fixing rollers come into contact, differs from the circumferential speed of the photosensitive drum. As a result, the conveyance speed around the drum is increased, resulting in the above-mentioned inconvenience.

In addition, especially when the fuser roller of the fuser unit of a small electrophotographic printer uses a molded type bearing instead of a bearing, the sliding resistance between this bearing and the rotation shaft of the fuser roller becomes large. If the fixing roller slips due to the situation or offset prevention oil, etc.,
The peripheral speed of the fixing roller decreases due to the impact when the leading edge of the transfer paper enters between the fixing rollers of the fixing device, so the conveyance speed at the leading edge of the transfer paper becomes lower than the conveyance speed around the photosensitive drum.
The same inconvenience as described above will occur.

The present invention has been made in view of the above problems.

The objective is to provide a fixing device that can always match the circumferential speed of the fixing roller of the fixing device with the circumferential speed of the photosensitive drum.

(Means for Solving the Problems) To achieve the above object, the present invention provides a fixing device for an image forming apparatus in which a pair of fixing rollers are rotationally driven by a drive device, in which the drive device is independently driven for driving the fixing rollers. The driving device is controlled by detecting the rotational speed of the fixing roller, and the circumferential speed of the fixing roller is controlled to match the circumferential speed of the image carrier, which is controlled to a constant value. It is characterized by

(Function) The circumferential speed of the fixing roller is controlled by detecting the rotational speed of the fixing roller and controlling the independently provided drive device.

Even if some change occurs in the circumferential speed of the fixing roller, the circumferential speed can be maintained at a constant value. Therefore, the circumferential speed of the image carrier and the fixing roller, which are controlled to a constant value, can be controlled to match.

(Example) An example of the present invention will be described below with reference to the accompanying drawings, taking a laser beam printer as an example.

First, the overall configuration of the laser beam printer will be explained with reference to FIG.

In the figure, a laser beam modulated according to an image signal is scanned and outputted from a scanner unit l including a laser, a polygon mirror, and a correction lens system,
The light is reflected and irradiated onto the photosensitive drum 3, which is an image carrier. The photosensitive drum 3 is uniformly charged by a primary charger 4 which is a corona discharger, and an electrostatic latent image is formed by irradiation with laser light. The electrostatic latent image is formed by the developer (
toner) 5a to form a toner image.

On the other hand, a transfer paper 7, which is a transfer material stored in a cassette 6, is fed by a paper feed roller 8 to a registration roller 9 in synchronization with the formation of an electrostatic latent image on the photosensitive drum 3. Furthermore, this transfer paper 7 is transferred to the photosensitive drum 3 by a registration roller 9.
The toner image on the photosensitive drum 3 is transferred to the transfer paper 7 by the transfer charger lO, which is a corona discharger, in synchronization with the leading edge of the electrostatic latent image formed thereon. . The transfer paper 7 with the toner image transferred thereto is transferred to the conveyance guide 1
1, the toner image is permanently fixed by the fixing device 12, and the toner image is discharged to the outside of the apparatus by the discharge roller 13.

Further, the toner remaining on the photosensitive drum 3 is removed by a cleaning device 14, and the charging history of the photosensitive drum 3 is then erased by a pre-exposure device 15, which is a corona discharger.

The photosensitive drum 3. -Charger 4. The developing device 5° cleaning device 14 is integrally housed in a cover 16 as an image forming unit (hereinafter referred to as process cartridge) K, and is configured to be detachable from the main body of the apparatus. Incidentally, the process cartridge K is provided with a drum protection cover 17 for shielding the photosensitive drum 3 from light so as not to cause light fatigue due to disturbance light hitting the photosensitive drum 3 when the process cartridge K is taken out of the apparatus main body.

The fixing device 12 includes a pair of rotatable fixing rollers 20 and 21.
are provided in pressure contact with each other, and the fixing roller 20 on the side that contacts the toner image on the transfer paper 7 is equipped with a heater and the like. Then, from the photosensitive drum 3 side, the fixing device 12
The transfer paper 7, which has been conveyed toward There is something that sticks and fixes on the paper 7.

Here, since the fixing device 12 and the photosensitive drum 3 are arranged close to each other, depending on the size of the transfer paper 7, the transfer paper 7
Even when the leading end of the transfer paper 7 enters the fixing device, the toner image from the photosensitive tram 3 may still be transferred to the rear end of the transfer paper 7, as shown in FIG. Therefore, the conveyance speed of the transfer paper 7 in the fixing device 12, that is, the circumferential speed of the fixing roller 20, 21, and the conveyance speed of the transfer paper 7 on the photosensitive drum 3, that is, the circumferential speed of the photosensitive tram 3 must be set equal. be.

Next is the fixing device according to the present invention! ! A first embodiment of No. 12 will be explained with reference to FIGS. 1 and 2.

FIG. 1 shows a perspective view of the fixing rollers 20 and 21 of the fixing device 12. The fixing roller 20 on the upper side in the figure has a heater installed therein and serves as a heating roller, and the fixing roller 20 on the lower side serves as a heating roller. The pressure roller 21 is pressed against the heating roller 20. A nip portion is formed in the contact portion 22 of the heating and pressure rollers 20 and 21, so that the toner image on the transfer paper can be easily fixed.

One of the heating and pressing rollers 20 and 21 in the axial direction includes a driving device 3 for rotationally driving the heating and pressing rollers 20 and 21.
0 is attached. The drive IItII 30 is provided at one end side of the heating and pressure rollers 20 and 21, and is a first roller having the same diameter and meshing with each other. A second gear 31 , 32 and a drive gear 3 that meshes with the first gear 31 to rotate the first gear 31 and also rotate the second gear via the first gear 31 .
3, a DC servo motor 35 that rotates the drive gear 33 at a constant speed via a drive shaft 34, and the like.

Further, the rotation shaft of the second gear 32, that is, the rotation shaft 21a of the pressure roller 21 extends outward, and an encoder 40 for detecting the rotation speed of the pressure roller 21 is attached to the end thereof. The encoder 4° includes a disc 41 that is attached to the end of the rotating shaft 21a and also functions as a flywheel;
It is composed of a photointerrupter 42 and the like that sandwich the outer periphery of the disk 41 and emit light through openings 41a, . , this encoder 40 emits light according to the rotation of the disc 41, and emits light through the opening 41a of the disc 41 via the light receiving element.
, -..., and the rotational speed of the pressure roller 21 can be detected. Note that since the heating roller 20 also rotates at the same speed as the pressure roller 21, detection of the rotational speed of the pressure roller 21 also serves as detection of the rotational speed of the heating roller 20.

Now, referring to FIG. 2, a means for controlling the rotational speed of the fixing rollers 20 and 21 of the fixing device 12 will be explained.

As described above, the rotational speed of the fixing roller 20.degree. 21 is controlled so that its circumferential speed coincides with the circumferential speed of the photosensitive tram 3.

In the figure, 50 is a speed command unit for instructing the speed value to be controlled, 51 is a first control circuit for controlling the speed of the fixing rollers 20 and 21, and 52 is a first control circuit for controlling the speed of the photosensitive drum 3. This is the second control circuit. Further, 53 is a DC servo motor that independently rotates the photosensitive tram 3.
54 is an encoder for detecting the rotational speed of the photosensitive tram 3.

Then, the speed command unit 50 instructs the same circumferential speed setting value so that the circumferential speeds of the fixing roller 20.21 and the photosensitive drum 3 are equal, and the first. Through the second control circuit 51.52 and the encoder 40.54, the DC servo motor 35.
The rotation speed of 53 is controlled to a constant value. On the other hand, if the circumferential speed of the fixing roller 20° 21 or the photosensitive drum 3 changes from the set value for some reason, the change will be caused by the encoder 40.
or 54, the rotational torque of the DC servo motor 35 or 53 is increased or decreased by the first or second control circuit 51 or 52, and the fixing rollers 20, 21 are immediately detected.
Alternatively, the photosensitive drum 3 is controlled so that its peripheral speed can return to the set value.

Therefore, even if the conveyance speed of the transfer paper 7 conveyed by the fixing device 12 changes due to the bearings of the fixing rollers 20, 21, etc.,
The fixing rollers 20 and 21 of the fixing device 12 are independent drive units!
30 and the speed control is performed independently, it is easy to restore the conveyance speed of the transfer paper 7 in the fixing device 12 to the set value and make it the same as the conveyance speed of the transfer paper 7 by the photosensitive drum. Become. As a result, the fixing roller 20°2
1 and the photosensitive tram 3 in the transfer area of the photosensitive drum 3 in the advancing direction of the transfer paper 7, and as shown in FIG. Inconveniences such as the transfer paper 7 coming into contact with the drum protection cover 17 of the process cartridge can be prevented.

Next, a second embodiment of the fixing device 12 according to the present invention will be described with reference to FIG.

It should be noted that devices having the same functions as the devices according to the first embodiment are given the same reference numerals as those according to the first embodiment in this embodiment, and their explanations will be omitted.

The difference between this embodiment and the first embodiment is that the encoder 40 for detecting the rotational speed of the fixing roller 12 is directly connected to the rotation shaft 21m of the pressure roller 21 in the first embodiment, but in this embodiment Now, this encoder 40A is connected to the fixing rollers 20 and 21.
This is provided on the drive shaft 34 that protrudes outward of the DC servo motor 35 for rotational driving.

Generally, the rotation speed of the DC servo motor 35 is higher than the rotation speed of the fixing rollers 20 and 21, so the number of teeth of the drive gear 33 is higher than the rotation speed of the DC servo motor 35. The number of teeth of the second gear 31 and 32 increases,
The rotation of the DC servo motor 35 is decelerated and the rotation of the fixing roller 20 is
, 21. On the contrary, this is true when the fixing rollers 20, 2
If the rotational speed on the first side changes for some reason, this change will be magnified and transmitted to the drive gear 33. Therefore, the change in the rotational speed of the fixing rollers 20 and 21 is caused by the drive shaft 34
Since the encoder 40A is enlarged and transmitted to the photointerrupter 42 via the disk 41 of the encoder 40A, the encoder 4 according to the present embodiment is smaller than the encoder 40 according to the #l embodiment.
With 0A, it is possible to more sensitively catch the speed fluctuations of the fixing rollers 20 and 21.
1 fine-grained control becomes possible.

The other parts are the same as in the first embodiment, and the same effects as in the first embodiment can be obtained in this embodiment as well.

Next, a third embodiment of the fixing device 12 according to the present invention will be explained with reference to FIGS. The same reference numerals as those related to the above will be given, and the explanation thereof will be omitted.

The difference between this embodiment and the first embodiment is that the encoder 40.53 and the first and second control circuits 51.52 are
A speed change rate calculation circuit 55 is provided between the two. The speed change rate calculation circuit 55 calculates the transfer paper conveyance speed Vt obtained from the encoder 53 via the rotation speed of the photosensitive drum 3, and the transfer paper conveyance speed obtained from the encoder 40 via the rotation speed of the fixing rollers 20 and 21. V, then the speed change rate S defined as s=(vl -v*)/vl''C' is calculated.Then, based on the speed change rate S, the first and second control circuits 51 .52 is configured to operate.

That is, as shown in FIG. 5, when the transfer paper conveyance rate V by the photosensitive drum 3 is approximately constant and the transfer paper conveyance speed v2 by the fixing rollers 20 and 21 is decreasing, for example, the speed change rate When S is less than 0.15, the first control circuit 51
The control of the DC servo motor 35, that is, the torque increase starts. As a result, vl and V substantially match after time T has passed after the start of control.

In this embodiment, the transfer paper conveyance speed V1. While constantly comparing V and V, make sure that the speed difference does not become too large.

And first. Second control circuit 51.52 DC servo motor 3
5.53 Encoders 40, 53 etc. control the transfer conveyance speed v, , V to match the speed determined by the speed command unit 50, so that the transfer paper conveyance speed in the fixing device 12 and the photosensitive drum 3 is controlled. The difference between Vl and V can always be kept within a certain value, and various troubles caused by differences in transfer paper conveyance speeds V, , V between the fixing device 12 and the photosensitive tram 3 can be solved by the first embodiment. This can be further suppressed.

In this embodiment, the encoder 40 of the fixing device 12 may be directly connected to the rotating shaft 21a of the pressure roller 21 as in the first embodiment, or may be provided by a DC servo motor as in the second embodiment. 35 may be directly connected to the drive shaft 34.

(Effect of the invention) Since the circumferential speed of the fixing roller is controlled to match the circumferential speed of the image carrier, which is controlled to a constant value, the front and rear ends of the transfer paper are connected to both the fixing device and the image carrier. Even when the image is transferred from the image carrier,
Inconveniences such as fluctuations in the transfer density in the direction of movement of the transfer paper, loops in the center of the transfer paper, and contact with the transfer paper or the protective cover of the process cartridge may cause the toner image on the transfer paper to be smeared. do not have.

[Brief explanation of drawings]

FIG. 1 is a perspective view of the main parts of the fixing device according to the first embodiment;
FIG. 2 is a control block diagram of the fixing device. 3 is a perspective view of the fixing device according to the second embodiment, FIG. 4 is a control block diagram of the fixing device according to the third embodiment, FIG. 5 is a diagram showing how the fixing device is controlled, and FIG. The figure is a side sectional view showing the entire mechanism of the laser beam printer. 3... Image carrier, 12... Fixing device, 20.21.
・・Fixing roller, 30-・・Drive device, 40.4OA・
...Encoder (fixing roller rotation speed detection). Patent Applicant Canon Co., Ltd. Agent Patent Attorney Ryo Yamashita - Figure 1 Figure 2

Claims (4)

[Claims] (1) In a fixing device of an image forming apparatus in which a pair of fixing rollers are rotationally driven by a drive device, the drive device is provided independently for driving the fixing rollers, and the rotational speed of the fixing rollers is detected. A fixing device characterized in that the driving device is controlled so that the circumferential speed of the fixing roller matches the circumferential speed of an image carrier, which is controlled to a constant value. (2) The fixing device according to claim 1, further comprising a rotation speed detector directly connected to the rotation shaft of one of the pair of fixing rollers to detect the rotation speed of the fixing roller. (3) The fixing device according to claim 1, wherein a rotation speed detector is provided directly connected to the drive shaft of the drive device, and the rotation speed of the fixing roller is detected via a signal from the rotation speed detector. . (4) A claim characterized in that the drive device is controlled via a control device that compares the circumferential speed of the fixing roller and the circumferential speed of the image carrier and maintains the difference between these circumferential speeds as small as possible. The fixing device according to items 1 to 3.